1.OA.B.3
Apply properties of operations as strategies to add and subtract. Students need not use formal terms for these properties. Examples: If 8 + 3 = 11 is known, then 3 + 8 = 11 is also known. (Commutative property of addition.) To add 2 + 6 + 4, the second two numbers can be added to make a ten, so 2 + 6 + 4 = 2 + 10 = 12. (Associative property of addition.)
Add using the make tens strategy. We can start with Unifix cubes, if necessary. For example, lay out Unifix cubes of length 2, 6, and 4. The student should recognize that 6 + 4 = 10, and from their work with teen numbers in Kindergarten, recognize that 10 + 2 = 12. Then we remove the Unifix cubes and ask the same question. Students are expected to say something like, 6 and 4 is 10, and I know 10 and 2 is 12, so the answer is 12.